1. Field of the Invention
The present invention relates to a process for producing a liquid ejection head provided with a piezoelectric substrate for ejecting a liquid such as an ink.
2. Description of the Related Art
A liquid ejection head provided with a piezoelectric substrate containing a piezoelectric material such as PZT (Pb(Zr,Ti)O3; lead zirconate titanate) is known.
In the liquid ejection head provided with the piezoelectric substrate, a groove is formed in the piezoelectric substrate, and a pressure chamber for applying an ejection pressure to an ink is formed by a wall of the groove and a member covering an opening of the groove. An electrode electrically connected to the head substrate is provided on an internal wall surface and an external wall surface of the groove. A voltage is applied to the electrode from the head substrate, whereby the wall of the groove is deformed to change a capacity of the pressure chamber and apply an ejection pressure to an ink within the pressure chamber, thereby ejecting an ink droplet from an ejection orifice communicated with the pressure chamber.
With the miniaturization of a recording apparatus provided with such a liquid ejection head, it is required to miniaturize the liquid ejection head. In order to miniaturize the liquid ejection head, thinner piezoelectric substrates have been developed.
However, the piezoelectric substrate is a relatively fragile brittle substrate. In a brittle substrate insufficient in thickness, there has been a possibility that when the brittle substrate is grasped with relatively strong force upon forming of a groove in the brittle substrate, the brittle substrate may be broken. Thus, Japanese Patent Application Laid-Open No. 2003-103787 and Japanese Patent No. 4565804 disclose a process for forming a groove in a brittle substrate without incurring breakage of the brittle substrate even when the brittle substrate is relatively thin.
Japanese Patent Application Laid-Open No. 2003-103787 discloses a process for forming a groove in a piezoelectric substrate as the brittle substrate. First, a support substrate harder than the piezoelectric substrate is provided. The support substrate is temporarily fixed on to one of two principal surfaces (surfaces facing in a thickness direction of the piezoelectric substrate) of the piezoelectric substrate so as not to cover a partial edge of said one principal surface. Then, the support substrate is grasped to conduct dicing from the partial edge of said one principal surface toward the other principal surface, thereby forming a plurality of grooves in the form of a comb. Thereafter, the piezoelectric substrate is bonded to a head substrate, and the support substrate is then separated from the piezoelectric substrate.
According to the process described in Japanese Patent Application Laid-Open No. 2003-103787, a relatively thin piezoelectric substrate is not broken upon the formation of the grooves because the piezoelectric substrate is not directly grasped.
Japanese Patent No. 4565804 discloses such a technique called WSS (Wafer Support System) that the thickness of a brittle substrate is reduced to a desired thickness. In WSS, a relatively thick brittle substrate is first provided as a substrate to be subjected to grinding, and the brittle substrate having a sufficient thickness is grasped to from a groove in the brittle substrate. Then, the brittle substrate is joined to a support substrate so as to cover one principal surface of the brittle substrate, and the other principal surface of the brittle substrate is ground to reduce the thickness of the brittle substrate. The brittle substrate is separated from the support substrate at the time of reaching a desired thickness.
According to the process described in Japanese Patent No. 4565804, the brittle substrate is not broken even when the brittle substrate is grasped with relatively strong force because the brittle substrate has the sufficient thickness when the groove is formed.
In recent years, a liquid ejection device has been used for a relatively large-sized recording medium. In order to produce a liquid ejection head capable of conducting large-size printing, there is a tendency to use a larger piezoelectric substrate in addition to reduction in the thickness of the piezoelectric substrate.
However, there has been a limit in such a large and thin piezoelectric substrate in the process described in Japanese Patent Application Laid-Open No. 2003-103787.
In the process described in Japanese Patent Application Laid-Open No. 2003-103787, the support substrate is temporarily fixed on to one principal surface of the piezoelectric substrate so as not to cover a partial edge of said one principal surface, and dicing is conducted from the edge portion of said one principal surface toward the other principal surface, thereby forming the grooves. Therefore, the edge portion of the piezoelectric substrate is bent in a thickness direction of the piezoelectric substrate upon the dicing. When the piezoelectric substrate is made large and thin, flexural rigidity of the piezoelectric substrate is lowered, so that there has been a possibility that the piezoelectric substrate may be broken due to curving in the thickness direction of the piezoelectric substrate.
In addition, Japanese Patent No. 4565804 only discloses an example where a silicon wafer was used as a substrate to be ground and does not disclose an application example where a piezoelectric substrate was provided as a substrate to be ground. If a piezoelectric substrate is used as a substrate to be ground, and the piezoelectric substrate can be made thinner, any supporting member is not provided on a principal surface different from the principal surface which has been joined to the support substrate. Accordingly, there has been a possibility that force in the thickness direction may be applied to the piezoelectric substrate thinned when the support substrate is separated from the piezoelectric substrate to break the piezoelectric substrate.